It was reported that GnuTLS does not check whether the two signature algorithms match on certificate import (CVE-2015-0294).
Kurt Roeckx discovered that decoding a specific certificate with very long DistinguishedName (DN) entries leads to double free. A remote attacker can take advantage of this flaw by creating a specially crafted certificate that, when processed by an application compiled against GnuTLS, could cause the application to crash resulting in a denial of service (CVE-2015-6251).